Cascade developing apparatus utilizing a rotary wheel with scoops

ABSTRACT

An apparatus for raising developer from a sump to an elevated position over an electrostatic plate bearing a latent image and cascading the developer over the plate to develop the image including a rotating frame having scoops fastened thereto which are filled with developer as they pass through the sump and empty the developer onto a guide member located at the elevated position which directs the developer over the plate. The scoops are independently mounted for rotation on the frame so that each can be orientated to its optimum position for emptying developer therein when at the elevated position.

United States Patent Adamek et al.

1451 Jan. 18, 1972 CASCADE DEVELOPING APPARATUS UTILIZING A ROTARY WHEEL WITH SCOOPS lnventors: John A. Adamek; Valdevutis C. Draugelis,

both of Rochester; George J. Oriel, Fairport, all of N.Y.

Assignee: Xerox Corporation, Rochester, NY.

Filed: Sept. 22, 1969 Appl. No.: 859,936

us. c1... ....3ss/3, 1 18/637 1m. (:1. ..G03g 15/00 Field of Search ....1 18/637, 312; 355/3; 198/103,

References Cited UNITED STATES PATENTS Fantuzzo ..355/3 3,470,999 10/1969 Snow 198/103 Primary Examiner-Samuel S. Matthews Assistant ExaminerRichard L. Moses Attorney-Donald F. Daley, James J. Ralabate and Robert W.

Mulcahy [5 7] ABSTRACT 5 Claims, 8 Drawing Figures PATENIEn JAN18l972 316235.553

sum 1 or 2 INVENTGFS JOHN A. ADAMEK VAIDEVUTIS C- DRNJGELIS BY as J. ORIE ATTORNEY PATENIEnJmmsn 3635553 SHEET 2 OF 2 i FIG. 40 FIG: 4b FIG. 4a

CASCADE DEVELOPING APPARATUS UTILIZING A ROTARY WHEEL WITI-I SCOOPS BACKGROUND OF TI-lE INVENTION This invention relates to cascade development and, more particularly, to raising developer from a sump to an elevated position over the development zone.

In many reproduction systems such as those utilizing the xerographic process, a latent electrostatic image is formed on an electrostatic plate and then developed with a suitable developer material. If a photosensitive plate is used, for example, the plate can be given a uniform charge and then exposed to a light pattern of the information to be reproduced. The areas of the plate struck by light are dissipated in charge resulting in a latent electrostatic charge pattern on the plate which can be developed by cascading developer material over the plate. A developer material commonly used in xerography consists of a finely-pulverized, pigmented resin powder called toner which is mixed with a coarser granular material made of or having a coating of a material which is remote from the toner in the triboelectric series so that the toner adheres to the carrier when the two are mixed. When the developer mixture is cascaded over a plate bearing a charge pattern, the toner particles are attracted from the carrier to the image areas of the plate by the electrostatic forces on the plate. The toner particles adhere to the plate in imagewise configuration thereby developing the latent image, while the carrier material is recirculated through the sump.

There are many known methods and apparatus by which the developing step can be performed. For instance, if the plate is planar and of moderate size, the developing step can be performed by placing the plate face upward in a tray having a reservoir of developer at one end and tilting the tray back and forth to pass the developer over the plate. However, the tilting tray is extremely unwieldy and it has been found that large plates can not be developed with satisfactory uniformity by this arrangement. In addition, such apparatus does not lend itself to continuous reproduction systems where the plate is in the shape of a rotatable drum.

For continuous reproduction systems, a conveyor system has been used to raise developer from a sump to the elevated position. The prior art conveyor systems have a flexible, rotatable, endless belt with small buckets attached to it which extend from the sump to the elevated position. As the belt is rotated, the buckets pass through the sump to gather developer and then upon reaching the elevated position dump the toner onto the plate. The buckets are usually riveted to the belt so thatthey are moved in a direction approximately perpendicular to the surface of the plate being developed.

One disadvantage with the belt-type system is that there is relatively poor cross-mixing of the developer across the plate; that is, a particular portion of developer is cascaded only over a particular zone of the plate as it is recirculated in the system due to the direction in which the buckets move relative to the plate. As a result of little cross-mixing, history effects are likely on the plate; for instance, if one zone of the drum requires a large amount of toner to develop the latent image while an adjoining zone requires relatively little amount of toner and if no interzonal cross-mixing can occur, the zone requiring a large amount of toner would soon run short of toner and not develop fully.

A second disadvantage with the conveyor system described above is that the developer is handled very roughly by the mechanism which tends to shorten the life of the carrier beads and decrease the triboelectrification between the carrierand toner. Another disadvantage with the'belt and bucket system is that the belt by its very nature tends to generate grit due to belt wear which enters the developing system and con taminates the constituents in the developer. The belt-type cascade system also tends to be bulky and complex in operation due to the large number of parts.

The, development apparatus described herein utilizes a rotatable frame located adjacent an electrostatic plate having scoops thereon which collect developer from the sump and raise it to an elevated position over the development zone where it is cascaded over the plate. The scoops move in a direction which is approximately parallel with the surface being developed so that cross-mixing of the developer is accomplished as the developer is circulated in the system. The present apparatus circulates the developer more gently throughout the development system than was possible in the prior art devices thereby preserving the life of the developer. The present apparatus is also simpler, less expensive to manufacture, and more dependable than prior art developer conveyor systems.

Accordingly, it is an object of this invention to improve cascade development to overcome the deficiencies of the prior art as described above.

It is a further object of the present invention to improve cascade development apparatus by assuring that the developer mixture is cross-mixed as developer circulates through the system.

A further object of the present invention is to improve cascade development apparatus so that the developer mixture is handled in a gentle manner to assure maximum life of the developer.

A further object of the present invention is to improve cascade development apparatusby making it simpler and less bulky than prior art systems.

SUMMARY OF THE INVENTION The present invention is a cascade development apparatus including a rotatable frame having a plurality of scoops mounted thereon which rotate through a sump of developer material and an elevated position. Each scoop contains an orifice through which developer can enter from the sump and be discharged at the elevated position to cascade over the plate. The apparatus contains a guide which directs developer discharged by the scoops into a development zone located adjacent the plate being developed.

In one embodiment of the invention, the scoops are independently rotated on the frame to enable each scoop to attain its optimum orientation relative to the frame for gathering developer from the sump and discharging it to the development zone. The scoops are biased to the optimum orientation for gathering developer from the sump and are rotated to the optimum orientation for discharging developer only as each passes through the elevated position.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be used in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of the inventionin a xerographic reproduction system;

FIG. 2 is an illustration of the invention alone;

FIG. 3 is a schematic illustrationof the preferred positions of the scoops relative to the frame;

FIG. 4a-c shows the various orientations of a scoop as it passes through the elevated position; and

FIGS. 5 and 6 are schematic illustrations of the mechanism which enables the scoops to rotate as they pass through the elevated position.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention described herein can be used to-raise any type of granular material to an elevated position, however, for the purpose of this disclosure, the invention isdescribed in conjunction with elevating developer from a sump to an elevated position in a cascade development system of a xerographic copier. FIG. 1 shows the development apparatus in a xerographic copier. The copier includes a photosensitive member 10, or plate, upon which a reproduction is formed, and several process stations, A-E, arranged about its periphery. The photosensitive member includes a rotatable drum 11, which rotates with shaft 12, having a conductive layer 13 and a photoconductive layer 14. A latent electrostatic image is formed on member 11 by passing through charging station A and exposing station B. The charging station can include any suitable means for placing a uniform charge on layer 14 such as a corona charging device 16. The exposure station B can include any suitable device 20 which projects a light image of the information to be reproduced on the surface of element in synchronism with the movement thereof. The light image projected onto the drum surface causes selected charge dissipation on illuminated areas of layer 14 and forms an electrostatic charge pattern on the drum conforming to the light image.

After the charging and exposing steps are completed, the photosensitive member passes through developing station 6 which is described in detail below. At the development station, toner is deposited on the surface of the plate in accordance with the charge pattern thereon. Following develop ment of the latent image with toner, the toner image is transferred from the plate to a web of paper 28, or the like, between guide rollers 29 and 31 which act to position the web against the plate. Transfer is carried out at station D and is accomplished with the aid of corotron 32 as web 28 is fed from reel 26 onto the plate and then rewound on reel 27. Fusing element 33 is positioned to heat the toner image on the web and thus, fix and permanently bond it to the paper web. Cleaning station E includes a rotating cylindrical brush 41 which contacts the plate subsequent to image transfer and is used to remove any residual image material from the surface of the plate after transfer is completed.

Any suitable process apparatus can be used in stations A, B, D, and E described above. In addition, any suitable drive means and control systems can be used to make the plate and process stations function in the manner described above. For example, a main machine motor (now shown) can be used to drive shaft 12 and, through suitable gearing arrangements, can operate the moving elements in the process stations.

The present invention is utilized in the development station C and is employed in conjunction with cascade development of the plate. In cascade development, a plate bearing a latent charge pattern is cascaded with a developer mixture to deposit toner particles on the plate in imagewise configuration. The developer usually comprises a mixture of finely divided, electroscopic, pigmented resinous powder, called toner, and a larger, granular material called carrier. The carrier is made of or coated with a material removed from the toner in the triboelectric series so that when the two are mixed, the toner particles adhere to the carrier particles through triboelectric action.

The developer mixture 52 is contained in the sump area 53 of the development housing 51 and is raised to an elevated position over the development zone, designated approximately by the brackets showing station C, and cascaded across the plate 10. After flowing through the development zone, the developer falls back into the sump area and is again raised to the elevated position. As toner is deposited on the plate by the cascading developer, additional toner is placed in the sump by toner dispenser 54 to assure that adequate toner is available to the plate at all times.

The apparatus for raising the developer from the sump to the elevated position, the elevated position being adjacent the development zone over guide 55 which is connected to the housing 51 in a stationary manner so as not to interfere with the drum or scoops includes conveyor apparatus 56 and drive apparatus 57. The conveyor apparatus comprises a rotatable frame 58 having a plurality of scoops 59 mounted thereon. The drive means comprises a motor 61 mounted on housing 51 having a drive shaft 62 which is attached to hub 63 which, in turn, is fastened to frame 58. The scoops contain an orifice 64 through which developer can enter and be discharged from the scoop. Motor 61 turns shaft 62 and the frame so that the scoops rotate towards the direction which their orifices face. In the apparatus shown in FIG. 1, the shaft 62 rotates in the direction shown by the arrow.

Referring to FIG. 2 which shows the development apparatus in more detail, the plate is driven by shaft 62 in a direction whereby orifices M'enable developer 52to flow into the scoop 59 as each scoop passes through the developer mixture contained in the sump of the housing. The conveyor apparatus is driven by shaft 62 at a constant speed of rotation so that uniform flow of developer is cascaded across the plate. As the frame 58 rotates each scoop is periodically dipped into or immersed in the developer and picks up a quantity of developer through its orifice. Developer enters the scoop since the orifices are located on the leading side of the scoops; that is, the side towards which the scoop is rotated. After passing through the sump of developer material, the scoop moves with the plate to an elevated position over the plate 10 and guide 55. When a scoop reaches the vicinity of its highest elevated position, to which it is brought by the frame, the developer in the scoop falls out of the scoop due to the force of gravity on the developer causing the developer to pass from the scoop onto guide 55 which directs it onto the plate 10. Each scoop on the frame acts in similar fashion generating a constant flow of developer mixture on the guide which, in turn, places a continuous flow of developer material across the surface of the plate 10.

Referring to FIG. 1, the conveyor apparatus shown as being operated in a plane which is inclined to the vertical. This manner of operation is preferred in that it facilitates the movement of developer material to and out of the scoop. In addition, mixing of the two constituents of the developer mixture is also aided which enables the toner particles and carrier beads to acquire a strong triboelectric charge which is desirable for good development. However, the conveyor apparatus can be operated in a vertical plane or any other plane which allows the developer to be elevated as described above.

As each scoop passes through the development housing sump, it causes a portion of the developer in the sump to move parallel to the surface of the plate as well as a portion to be picked up by the scoop. Such developer movement is very desirable, especially in a circulating development system since it causes interzonal mixing of developer across the width of the plate 10. If such interzonal mixing were not possible, history effects would become prevalent as development continued. For instance, if a first zone of the plate 10 consistently required a great deal more toner to develop the latent image than a second zone somewhat removed from it, the portion of developer mixture in the sump serving to develop the first zone of the plate would soon be depleted of toner while the second portion continues to maintain adequate toner. If additional toner is added to the sump, the first zone would have adequate toner, but there would be an excess of toner in the developer serving the second zone of the plate. This problem is eliminated by scooping the toner in a plane substantially parallel to the surface of the plate since this action produces a cross-mixing throughout the developer sump which tends to average the incidence of toner across the sump.

The orientation of the scoops on the frame must be such that each scoop can pick up developer from the sump and discharge developer from the elevated position. Referring to FIG. 3, in conjunction with the following discussion. it can be seen that the optimum scoop positions for pick up and discharge of developer are not the same. Assuming that the top of the frame 58 represents the elevated position where developer in a scoop is to be discharged and the bottom of the frame represents the position where a scoop picks up developer, the scoops are oriented at two angles in each position, a first angle shown in solid lines and a .second angle shown in dotted lines.

The optimum orientation of the scoop for picking up developer is shown in solid lines at both the top and bottom of the frame. This orientation, which is indicated by an angle X from a radial line drawn through the center of the frame, is considered optimum because the orifice of the scoop is facing downward into the sump of developer and allowing the developer to be easily gathered in the scoop as it rotates.

When a scoop in this orientation reaches the discharge position at the top of the frame, however, the orifice is not oriented for easy discharge of the scoop contents. The orifice faces upward from the sump, as shown by the scoop in solid lines at the top of the frame, and it is highly unlikely that all the developer contained therein would be discharged.

The optimum orientation for a scoop to discharge developer at the top of the frame is shown in dotted lines. In this orientation the orifice faces downward towards the sump enabling the developer to fall out of the scoop easily. When a scoop in this orientation passes through the sump, its orifice faces upward, as shown at the bottom of the frame in dotted lines, which is not optimum orientation for picking up developer.

It has been found that if the scoop is to be fixed on the frame, the best orientation for picking up developer, the plane of the orifice shown tilted at an angle X from a radial line, and the best orientation for discharging developer, the plane of the orifice shown tilted at an angle Y from a radial line, can be traded off to maximize the effects of both functions. After testing the device, it was found that the optimum picking up and discharging for a fixed scoop orientation occurred when the plane of the orifice was tilted in the direction shown by the scoop in dotted lines, but to a lesser degree. This preferred orientation is schematically illustrated in FIG. 3 by the scoop with double lines, wherein the angle Z at which the plane of the orifice is tilted from a radial line is in the same direction as Y, but at a smaller angle than Y.

In the alternative, the scoops can be mounted on the frame so that they are able to change their respective orientations relative to a radial line as needed. FIGS. 4-6 show one possible device for controlling the orientation of the scoops although any suitable control device could be used. In FIGS. 412-40 most favorable to picking up developer in all positions but that in the vicinity of the top of the frame. As a scoop containing a quantity of developer nears the elevated position near the top of the frame, it rotates in the counterclockwise direction relative to the frame, as shown by the arrow in FIG. 4a, to attain its optimum orientation for discharging developer. As can be seen by FIG. 4b, this orientation is similar to that shown by dotted lines in FIG. 3. The orientation shown in FIG. 4b is maintained by the scoop at the top of the frame until all of the developer contained by it has passed through the orifice and onto the guide (not shown) below. Then, the scoop, which has been rotated, is allowed to return, as shown by the arrow in F IG. 40, to its biased position before passing through the sump again. Of course, the scoops outside the vicinity of the top of the frame remain in their biased orientation during this time, as shown by the scoop at the bottom of the frame in FIGS. 4(1-4011.

The mechanism for rotating the scoops selectively in this manner is shown in FIGS. 5 and 6. Scoop 59 is mounted on rotatable shaft 71 which, in turn, is mounted for rotation on frame 58. The shaft 71, on the end opposite the scoop, has two rigid arms 72 and 73. Arm 72 is connected to arm 74, which is fastened to the frame by a spring 76, which biases the shaft 71 in the counterclockwise direction in FIG. 6, and the scoop in the clockwise direction as seen in FIGS. la-4c.

Arm 74 is attached to the machine frame and protrudes into the path of arm 73 as the scoop is rotated to the top of the frame. When arm 73 strikes arm 74, the shaft 71 rotates in the clockwise direction, as shown in FIG. 6, thereby rotating the scoop to its discharge position as seen in FIGS. 4a and 4b against the bias of spring 76. After the arm 73 has rotated past arm 74, which is after the scoop has discharged its developer, spring bias 76 causes shaft 71 to rotate in the counterclockwise direction, as seen in FIG. 6, and the scoop to reorient itself in its biased position, as seen in FIG. 4c.

In addition to the apparatus outlined above, many other modifications and/or additions to this invention will be readily apparent to those skilled in the art upon reading this disclosure, and these are intended to be encompassed within the scope of the invention.

What is claimed is:

1. In a reproduction system having a rotatable, photosensitive drum, means for forming a latent electrostatic image on the surface of the drum conforming to the information to be reproduced, means to cascade developer from an elevated position through a development station adjacent the surface of the drum and means to rotate successive increments of the drum surface through the development station to develop the latent image thereon, the improvement comprising an apparatus for raising developer from a sump containing developer to the elevated position at which it is cascaded through the development station comprising:

a. a circular frame mounted in a rotatable manner about a single axis such that said frame moves between the developer sump and the elevated position;

b. a plurality of scoops, each having an orifice on one side thereof through which developer can enter into the scoop as it passes through the sump and can be discharged from the scoop due to the gravity as it passes through the elevated position and each mounted on the frame so that upon rotation, the leading edge of each scoop is the side containing the orifice; and

c. means to rotate the frame so that the scoops pick up developer in the sump and carry it to the elevated position where it is discharged to the development station.

2. The apparatus of claim 1 wherein the frame is rotated in a plane which is substantially parallel to the surface of the drum whereby the developer is cross-mixed.

3. The apparatus in claim 2 wherein the frame is rotated in a plane which is inclined relative to the vertical plane so that the portion of the frame in the elevated position is closer to the surface of the drum than the portion of the frame in the sump[ 4. The apparatus in claim 1 further including a guide means between the scoops in the elevated position and the top of the development station which is inclined down towards the top of the development station adapted to guide developer discharged from the scoops into the development station.

5. In a reproduction system having a rotatable, photosensitive drum, means for forming a latent electrostatic image on the surface of the drum conforming to the information to be reproduced, means to cascade the developer from an elevated position through a development station adjacent the surface of the drum and means to rotate successive increments of the drum surface through the development station to develop a latent image thereon, the improvement comprising an apparatus for raising developer from a sump containing developer to an elevated position at which it is cascaded through the development station comprising:

a. a rotatable frame between the developer sump and elevated position;

b. a plurality of scoops rotatably mounted on the frame in a location where they pass through the developer sump and elevated position as the frame is rotated, each scoop having an orifice on one side thereof enabling developer to enter the scoop as it passes through the sump and to discharge from the scoop due to gravity as it passes through the elevated position;

c. means to rotate the frame so that the scoops pick up developer in the sump and carry it to the elevated position where it is discharged over the development station;

. each scoop being biased in an orientation relative to the frame so that as the frame rotates the leading side of each scoop outside the vicinity of the elevated position is the side of the scoop containing the orifice; and

e. means to rotate each scoop relative to the frame only in the vicinity of the elevated position so that the side of the scoop containing the orifice substantially faces the sump thereby facilitating the discharge of the developer to the development station due to gravity when the scoops are in the elevated position. 

1. In a reproduction system having a rotatable, photosensitive drum, means for forming a latent electrostatic image on the surface of the drum conforming to the information to be reproduced, means to cascade developer from an elevated position through a development station adjacent the surface of the drum and means to rotate successive increments of the drum surface through the development station to develop the latent image thereon, the improvement comprising an apparatus for raising developer from a sump containing developer to the elevated position at which it is cascaded through the development station comprising: a. a circular frame mounted in a rotatable manner about a single axis such that said frame moves between the developer sump and the elevated position; b. a plurality of scoops, each having an orifice on one side thereof through which developer can enter into the scoop as it passes through the sump and can be discharged from the scoop due to the gravity as it passes through the elevated position and each mounted on the frame so that upon rotation, the leading edge of each scoop is the side containing the orifice; and c. means to rotate the frame so that the scoops pick up developer in the sump and carry it to the elevated position where it is discharged to the development station.
 2. The apparatus of claim 1 wherein the frame is rotated in a plane which is substantially parallel to the surface of the drum whereby the developer is cross-mixed.
 3. The apparatus in claim 2 wherein the frame is rotated in a plane which is inclined relative to the vertical plane so that the portion of the frame in the elevated position is closer to the surface of the drum than the portion of the frame in the sump.
 4. The apparatus in claim 1 further including a guide means between the scoops in the elevated position and the top of the development station which is inclined down towards the top of the development station adapted to guide developer discharged from the scoops into the development station.
 5. In a reproduction system having a rotatable, photosensitive drum, means for forming a latent electrostatic image on the surface of the drum conforming to the information to be reproduced, means to cascade the developer from an elevated position through a development station adjacent the surface of the drum and means to rotate successive increments of the drum surface through the development station to develop a latent image thereon, the improvement comprising an apparatus for raising developer from a sump containing developer to an elevated position at which it is cascaded through the development station comprising: a. a rotatable frame between the developer sump and elevated position; b. a plurality of scoops rotatably mounted on the frame in a location where they pass through the developer sump and elevated position as the frame is rotated, each scoop having an orifice on one side thereof enabling developer to enter the scoop as it passes through the sump and to discharge from the scoop due to gravity as it passes through the elevated position; c. means to rotate the frame so that the scoops pick up developer in the sump and carry it to the elevated position where it is discharged over the development station; d. each scoop being biased in an orientation relative to the frame so that as the frame rotates the leading side of each scoop outside the vicinity of the elevated position is the side of the scoop containing the orifice; and e. means to rotate each scoop relative to the frame only in the vicinity of the elevated position so that the side of the scoop containing the orifice substantially faces the sump thereby facilitating the discharge of the developer to the development station due to gravity when the scoops are in the elevated position. 